Dual trench isolation for CMOS with hybrid orientations

ABSTRACT

The present invention provides a semiconductor structure in which different types of devices are located upon a specific crystal orientation of a hybrid substrate that enhances the performance of each type of device. In the semiconductor structure of the present invention, a dual trench isolation scheme is employed whereby a first trench isolation region of a first depth isolates devices of different polarity from each other, while second trench isolation regions of a second depth, which is shallower than the first depth, are used to isolate devices of the same polarity from each other. The present invention further provides a dual trench semiconductor structure in which pFETs are located on a (110) crystallographic plane, while nFETs are located on a (100) crystallographic plane. In accordance with the present invention, the devices of different polarity, i.e., nFETs and pFETs, are bulk-like devices.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 11/877,048, filed Oct. 23, 2007, now U.S. PatentApplication Publication No. 2008/0036028, which is a divisionalapplication of U.S. patent application Ser. No. 11/207,216, filed Aug.19, 2005, now U.S. Patent Application Publication No. 2007/0040235. Thisapplication is related to co-assigned U.S. patent application Ser. Nos.10/799,380, filed Mar. 12, 2004, now U.S. Pat. No. 7,023,057, Ser. No.10/696,634, filed Oct. 29, 2003, now U.S. Pat. No. 7,023,055, and Ser.No. 10/250,241, filed Jun. 23, 2003, now U.S. Pat. No. 7,329,923, theentire contents of each application are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to high-performance metal oxidesemiconductor field effect transistors (MOSFETs) for digital and analogapplications, and more particular to MOSFETs utilizing carrier mobilityenhancement from surface orientation in which a dual trench isolationdesign is employed. Specifically, a first trench isolation region havinga first depth is used to isolate nFETs from pFETs, while second trenchisolation regions having a second depth, which is shallower than thefirst depth, are used to isolate nFETs from nFETs and pFETs from pFETs.

BACKGROUND OF THE INVENTION

In present semiconductor technology, complementary metal oxidesemiconductor (CMOS) devices, such as nFETs or pFETs, are typicallyfabricated upon semiconductor wafers, such as Si, that have a singlecrystal orientation. In particular, most of today's semiconductordevices are built upon Si having a (100) crystal orientation.

Electrons are known to have a high mobility for a (100) Si surfaceorientation, but holes are known to have high mobility for a (110)surface orientation. That is, hole mobility values on (100) Si areroughly 2×-4× lower than the corresponding electron mobility for thiscrystallographic orientation. To compensate for this discrepancy, pFETsare typically designed with larger widths in order to balance pull-upcurrents against the nFET pull-down currents and achieve uniform circuitswitching. pFETs having larger widths are undesirable since they take upa significant amount of chip area.

On the other hand, hole mobilities on (110) Si are 2× higher than on(100) Si; therefore, pFETs formed on a (110) surface will exhibitsignificantly higher drive currents than pFETs formed on a (100)surface. Unfortunately, electron mobilities on (110) Si surfaces aresignificantly degraded compared to (100) Si surfaces.

As can be deduced from the above discussion, the (110) Si surface isoptimal for pFET devices because of excellent hole mobility, yet such acrystal orientation is completely inappropriate for nFET devices.Instead, the (100) Si surface is optimal for nFET devices since thatcrystal orientation favors electron mobility.

Methods have been described to form planar hybrid substrates withdifferent surface orientations through wafer bonding. In such endeavors,the planar hybrid substrate is obtained mainly throughsemiconductor-to-insulator, or insulator-to-insulator wafer bonding toachieve pFETs and nFETs on their own optimized crystal orientation forhigh performance device manufacture. However, at least one type ofMOSFET (either pFETs or nFETs) is on a semiconductor-on-insulator (SOI),while the other type of MOSFET is either on a bulk semiconductor or anSOI with a thicker SOI film.

A method to fabricate planar bulk-like nFETs and pFETs on a hybridorientated substrate through silicon-to-silicon direct bonding toachieve both kinds of devices on their optimized orientation for highestperformance has been disclosed, for example, in U.S. application Ser.Nos. 10/799,380, filed Mar. 12, 2004 and 10/696,634, filed Oct. 29,2003.

In today's conventional CMOS integrated circuits (ICs) with bulk-likepFETs and nFETs, isolation usually is achieved by shallow trenchisolation (STI). Such a structure is shown, for example, in FIG. 1. Inthe prior art structure, reference numeral 100 denotes the semiconductorsubstrate, reference numeral 102 denotes a p-well, reference numeral 104denotes an n-well, reference numeral 106 denotes shallow trenchisolation (STI), reference numeral 108 denotes an nFET, referencenumeral 110 denotes a pFET, reference numeral 112 denotes a p-well (orsubstrate) contact and reference numeral 114 denotes an n-well (orsubstrate) contact.

In the prior art structure shown in FIG. 1, each STI 106 is formed byfirst etching relatively shallow trenches (on the order of about 0.3 toabout 0.5 μm), which are shallower than the depth of the well, into thesemiconductor substrate 100 and then each trench is filled with a trenchdielectric material such as an oxide. The surface is planarized aftertrench fill to complete the isolation structure. However, as the groundrule shrinks, the width of the STI reduces, resulting in a higher aspectratio. Thus, it has become more difficult to obtain void- and seam-freetrench fill.

On the other hand, CMOS isolation exists not only between like-kind ofdevices, e.g., between two nFETs or two pFETs, but also between oppositepolarity, i.e., between nFETs and pFETs which are separated by at leastone well. In general, isolation for the latter, including nFET and pFETisolation and latch-up, consumes much more chip area and requires muchdeeper STI depth.

In view of the above discussion, there is a need for providing astructure having both pFETs and nFETs on a hybrid oriented (HOT)substrate with different crystal orientations, wherein both the pFET andnFET devices are bulk-like, and wherein the pFET and nFET devices areseparated from devices with opposite polarity.

SUMMARY OF THE INVENTION

The present invention provides a semiconductor structure in whichdifferent types of devices are located upon a specific crystalorientation of a hybrid substrate that enhances the performance of eachtype of device. In the semiconductor structure of the present invention,a dual trench isolation scheme is employed whereby a first trenchisolation region of a first depth isolates devices of different polarityfrom each other, while second trench isolation regions of a seconddepth, which is shallower than the first depth, are used to isolatedevices of the same polarity from each other.

The present invention further provides a dual trench semiconductorstructure in which pFETs are located on a (110) crystallographic plane,while nFETs are located on a (100) crystallographic plane. In accordancewith the present invention, the devices of different polarity, i.e.,nFETs and pFETs, are bulk-like devices.

In broad terms, the semiconductor structure of the present inventioncomprises:

a hybrid oriented substrate having at least two coplanar surfaces ofdifferent crystallographic orientation, said surfaces defining at leasta first device region and a second device region;

a first trench isolation region of a first depth separating said firstdevice region from said second device region; and

a plurality of second trench isolation regions of a second depth whichis shallower than the first depth located in each of said first andsecond device regions, whereby said first trench isolation region isemployed in separating semiconductor devices of different polarity fromeach other and said plurality of second trench isolation regions areemployed in separating semiconductor devices of the same polarity fromeach other.

The present invention further includes the semiconductor structure asdefined above in which first semiconductor devices of a first polarityare located in the first device region and second devices of a secondpolarity which are opposite from the first polarity devices are locatedin the second device region. The semiconductor devices employed in thepresent invention are typically nFETs and pFETs. When such semiconductordevices are used, the first trench isolation region (having the deeperdepth of the two isolation regions) is used in separating nFETs frompFETs, while the second trench isolation regions (having the shallowerof the two trench depths) are used in separating like-kind devices,i.e., nFETs from nFETs and pFETs from pFETs.

In addition to semiconductor structures, the present invention alsorelates to methods of forming such structures. In broad terms, themethod of the present invention comprises the steps of:

providing a hybrid substrate comprising a first lower semiconductorlayer of a first crystallographic orientation and a second uppersemiconductor layer of a second crystallographic orientation whichdiffers from the first crystallographic orientation, wherein aconductive bonding interface separates said semiconductor layers fromeach other;providing at least one opening of a first depth in said hybrid substratewhich exposes said first lower semiconductor layer;forming a spacer within said at least one opening having said firstdepth;regrowing a semiconductor material on said exposed first lowersemiconductor layer, said semiconductor material having said firstcrystallographic orientation;planarizing said semiconductor material to an upper surface of saidsecond upper semiconductor layer to provide a structure having at leasttwo coplanar surfaces of different crystallographic orientation; andforming trench isolation regions having a second depth which isshallower than the first depth of said opening in said at least twocoplanar surfaces, wherein said spacer provides isolates between thecoplanar surfaces of different crystallographic orientations.

In accordance with the present invention, the method of the presentinvention further comprises forming first semiconductor devices having afirst polarity on one of said coplanar surfaces of differentcrystallographic orientation and forming second semiconductor deviceshaving a second polarity on the other coplanar surface. Thus, nFETs canbe built into one of the crystallographic surfaces, while pFETs can bebuilt into the other crystallographic surface. In accordance with thepresent invention, the pFETs are built into a crystal surface thatprovides those kinds of FETs with optimal performance (usually a (110)crystallographic plane) and the nFET are built into a crystal surfacethat provides those kinds of devices with optimal performance (usually a(100) crystal plane). When such semiconductor devices are formed, thespacer within the opening defines a first trench isolation region ofsaid first depth that isolates nFETs from pFETs, while the shallowtrench isolations of said second depth define second trench isolationregions that separate nFETs from nFETs and pFETs from pFETs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation (through a cross sectional view)illustrating a prior art structure including MOSFETs on a bulk substratein which isolation between nFET and nFET, pFET and pFET, and nFET andpFET is done simultaneously.

FIG. 2 is a pictorial representation (through a cross sectional view)showing a hybrid substrate that can be employed in the present inventionhaving different surface orientations which is obtained bysemiconductor-to-semiconductor direct bonding.

FIGS. 3-6 are pictorial representations (through cross sectional views)showing the basic processing steps that are employed in the presentinvention using the hybrid substrate shown in FIG. 2 as the startingsubstrate. Note that in the inventive process deeper trench isolationhas been formed between nFETs and pFETs.

FIG. 7 is a pictorial representation (through a cross sectional view)showing shallower trench isolation located between like-kind FETs.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which relates to dual trench isolation for CMOSdevices located on a hybrid oriented substrate, will now be described ingreater detail by referring to the drawings that accompany the presentapplication. It is noted that the drawings of the present invention areprovided for illustrative purposes and thus they are not drawn to scale.

Reference is first made to FIG. 2 which shows an initial hybridsubstrate 10 having different crystal orientations that can be employedin the present invention. Specifically, the hybrid substrate 10 includesa first (i.e., bottom) semiconductor layer 12 and a second (i.e., top)semiconductor layer 16 having a bonding interface 14 locatedtherebetween. In accordance with the present invention, the firstsemiconductor layer 12 has a first crystallographic orientation and thesecond semiconductor layer 16 has a second crystallographic orientationwhich differs from that of the first crystallographic orientation.

The first semiconductor layer 12 of the hybrid substrate 10 is comprisedof any semiconductor material including, for example, Si, SiC, SiGe,SiGeC, Ge, GaAs, InAs, InP as well as other III/V or II/VI compoundsemiconductors. Combinations of the aforementioned semiconductormaterials are also contemplated herein. The first semiconductor layer 12may be strained, unstrained, or a combination of strained and unstrainedlayers can be used. Typically, the first semiconductor layer 12 is aSi-containing semiconductor material.

The first semiconductor layer 12 is also characterized as having a firstcrystallographic orientation which may be, for example, (110), (111), or(100). The first semiconductor layer 12 may optionally be formed on topof a handling wafer.

The thickness of the first semiconductor layer 12 may vary and is notcritical for practicing the present invention. Typically however, thefirst semiconductor layer 12 is a bulk handle wafer, its thickness isthe thickness of a wafer.

The second semiconductor layer 16 is comprised of any semiconductingmaterial which may be the same or different from that of the firstsemiconductor layer 12. Thus, the second semiconductor layer 16 mayinclude, for example, Si, SiC, SiGe, SiGeC, Ge, GaAs, InAs, InP as wellas other III/V or II/VI compound semiconductors. The secondsemiconductor layer 16 may also include combinations of theaforementioned semiconductor materials. Second semiconductor layer 16may also be strained, unstrained or a combination of strained andunstrained layers can be used, e.g., strained Si on relaxed SiGe.Typically, the second semiconductor layer 16 is comprised of aSi-containing semiconductor material.

The second semiconductor layer 16 is also characterized as having asecond crystallographic orientation, which is different from the firstcrystallographic orientation. Thus, the crystallographic orientation ofthe second semiconductor layer 16 can be, for example, (100), (111), or(110) with the proviso that the crystallographic orientation of thesecond semiconductor layer 16 is not the same as the crystallographicorientation of the first semiconductor layer 12.

The thickness of the second semiconductor layer 16 may vary depending onthe initial starting wafer used to form the hybrid substrate 10.Typically, however, the second semiconductor layer 16 has a thicknessfrom about 50 nm to about 200 μm, with a thickness from about 150 nm toabout 2 μm being more highly preferred.

The bonding interface 14 that is present between the first semiconductorlayer 12 and the second semiconductor layer 16 is conductive. Thebonding interface 14 typically has a thickness from about 10 nm or less.The thickness of the bonding interface 14 is determined by the bondingprocess used.

The exact crystal orientations of the first semiconductor layer 12 andthe second semiconductor layer 16 may vary depending on the material ofthe semiconductor layers as well as the type of semiconductor devicesthat will be subsequently formed thereon. For example, when Si isemployed as the semiconductor material, electron mobility is higher on a(100) surface orientation, and hole mobility is higher on a (110)surface orientation. In this case, the (100) Si surface is used as thedevice layer for nFETs, while the (110) Si surface is used as the devicelayer for pFETs.

The hybrid substrate 10 shown in FIG. 2 is formed in the presentinvention through semiconductor-to-semiconductor direct bonding. In sucha process, two semiconductor substrates or wafers are directly bondedtogether without the presence of an insulating layer therebetween. Thetwo wafers used in fabricating the hybrid substrate 10 may include twobulk semiconductor wafers, a bulk semiconductor wafer and a wafercontaining an etch stop layer and a handling wafer, or a first bulkwafer and a second bulk wafer which includes an ion implant region, suchas a hydrogen implant (i.e., H₂) region, which can be used to split aportion of at least one of the wafers during bonding.

In some embodiments of the present invention the bonding processdescribed in U.S. Ser. No. 10/250,241, the entire content of which isincorporated herein by reference, can be employed.

To achieve a good conductive bonding interface 14 throughsemiconductor-to-semiconductor direct wafer bonding, it is usually, butnot always, required to perform a surface treatment step on at leastone, preferably both, of the wafers, before bonding to obtain eitherhydrophilic or hydrophobic surfaces.

Hydrophobic surfaces can be achieved, for example, by utilizing a HF dipprocess such as disclosed in S. Bengtsson, et al., “Interface chargecontrol of directly bonded silicon structures”, J. Appl. Phys. V66, p1231, (1989), while hydrophilic surfaces can be achieved by either a dryclean process, such as, for example, an oxygen plasma (See, S. Farrens,“Chemical free room temperature wafer to wafer bonding”, J. Electrochem.Soc. Vol 142, p 3949, (1995); an argon high-energy beam surface etching,and/or a wet chemical oxidizing acid such as H₂SO₄ or HNO₃ solution. Thewet etching process is disclosed, for example, in M. Shimbo, etc.“Silicon-to-silicon direct bonding method”, J. Appl. Phys. V60, p 2987(1986).

Although hydrophobic surfaces may provide better electronic properties,hydrophilic surfaces may provide sufficient conductivity because thenative oxide present at the bonding interface 14 is usually only 2-5 nm.Moreover, substrates formed by the direct bonding of two hydrophilicsurfaces tend to have a large leakage current. Furthermore, crystallinejunctions can be formed after a high-temperature anneal step isperformed to further enhance the current flow across the bondinginterface 14.

Direct semiconductor-to-semiconductor wafer bonding (with or without thesurface treatments mentioned above) is achieved in the present inventionby first bringing the two wafers having different crystal orientationsinto intimate contact with other, optionally applying an external forceto the contacted wafers, and then optionally annealing the two contactedwafers under conditions that are capable of increasing the bondingenergy between the two wafers. The annealing step may be performed inthe presence, or absence, of an external force. Bonding is achievedtypically during the initial contact step at nominal room temperature.By nominal room temperature, it is meant a temperature from about 15° C.to about 40° C., with a temperature of about 25° C. being morepreferred.

After bonding, the wafers are typically annealed to enhance the bondingstrength and improve the interface property. The annealing temperatureis typically carried out at a temperature from about 900° to about 1300°C., with an annealing temperature from about 1000° to about 1100° C.being more typical. Annealing is performed within the aforementionedtemperature ranges for various time periods that may range from about 1hour to about 24 hours. The annealing ambient can be O₂, N₂, Ar, or alow vacuum, with or without external adhesive forces. Mixtures of theaforementioned annealing ambients, with or without an inert gas, arealso contemplated herein.

Although high-temperature annealing (as described above) is often used,it is also possible to use a low temperature anneal (less than 900° C.)which can also achieve good mechanical and electrical properties.

It should be noted that the annealing step that follows the directsemiconductor-to-semiconductor bonding step can be performed at a singletemperature using a specific ramp-up rate, or it can be performed usingvarious temperatures in which various ramp-up rates and soak cycles areemployed.

To obtain a certain predetermined thickness of the second semiconductorlayer 16, various layer transfer techniques can be used in the presentinvention. One direct and simple approach that can be used in thepresent invention is to use wafer grinding, polishing or an etch backprocess. To provide better control of the layer transfer process, anetch stop layer located between second semiconductor layer 16 and ahandling wafer can be used; the etch stop layer and the handling waferare both removed after wafer bonding. The etch stop layer can be aninsulator, such as an oxide, nitride or oxynitride, which means thestarting top wafer may be an SOI substrate. Alternatively, the etch stoplayer can be another semiconductor material which can be removedselectively from the second semiconductor layer 16 after bonding andalso serves as an etch stop to remove the handling wafer.

Another layer transfer technique, applicable to embodiments where one ofthe wafers includes an ion implant region. In this case, the ion implantregion forms a porous region which causes a portion of the wafer abovethe ion implant region to break off leaving a bonded wafer. The implantregion is typically comprised of hydrogen ions that are implanted intothe surface of one of the wafers utilizing ion implantation conditionsthat are well known to those skilled in the art. After bonding, aheating step is typically performed in an inert ambient at a temperaturefrom about 100° to about 400° C. for a time period from about 2 to about30 hours to increase the bonding energy. More preferably, the heating isperformed at a temperature from about 200° to about 300° C. for a timeperiod from about 2 to about 20 hours. The term “inert ambient” is usedin the present invention to denote an atmosphere in which an inert gas,such as He, Ar, N₂, Xe, Kr or a mixture thereof, is employed. Apreferred ambient used during the bonding process is N₂. The layersplitting at the implant region will take place during a 350°-500° C.annealing afterwards.

The hybrid substrate 10 shown in FIG. 2 is used as the startingsubstrate for the method of the present invention that is depicted inFIGS. 3-7. The process flow depicted in these drawings will now bedescribed in greater detail.

After providing the hybrid substrate 10 shown in FIG. 2, a hard mask,i.e., pad stack, 18 is formed on an exposed upper surface of the secondsemiconductor layer 16 utilizing a deposition process such as, forexample, chemical vapor deposition (CVD), plasma-enhanced chemical vapordeposition (PECVD), chemical solution deposition, atomic layerdeposition, or physical vapor deposition. Alternatively, the hard mask18 can be formed utilizing a thermal oxidation, nitridation oroxynitridation process.

The hard mask 18 is composed of a dielectric material such as, forexample an oxide, nitride, oxynitride or a multilayered stack thereof.The thickness of the hard mask 18 may vary depending on the compositionof the mask material as well as the technique that was used in formingthe same. Typically, the hard mask 18 has, an as deposited thickness,from about 5 to about 500 nm.

The hybrid substrate 10 including the hard mask 18 is then patterned bylithography and etching to provide a patterned structure such as shown,for example, in FIG. 3. As shown, at least one opening 20 is provided inthe hybrid substrate 10 including the hard mask 18 that exposes aportion of the first semiconductor layer 12. The lithographic stepincludes applying a photoresist to the hard mask 18, exposing thephotoresist to a desired pattern of radiation and developing the patterninto the exposed photoresist utilizing a conventional resist developer.The etching step used in forming the structure shown in FIG. 3 may beperformed utilizing a single etching process or multiple etching stepsmay be employed. The etching may include a dry etching process such asreactive-ion etching, ion beam etching, plasma etching or laser etching,a wet etching process wherein a chemical etchant is employed or anycombination thereof.

In accordance with the present invention, the etching depth of theopening 20 can be designed to match the requirement of isolation betweenopposite polarity devices, i.e., between nFETs and pFETs. The blocklevel lithography used in providing the structure shown in FIG. 3, whichdefines the area of the nFETs and pFETs, has large features, usuallyseveral times larger than the critical dimension, and thus the at leastone opening 20 does not have as high an aspect ratio as a normal litholevel which defines the active area.

In the structure shown in FIG. 3, the area of the hybrid substrate 10that is protected by the patterned hard mask 18 is referred to herein asa first device region 50, while the area that is etched and was thus notprotected by the patterned hard mask 18 is referred to as a seconddevice region 52. In accordance with the present invention, the firstdevice region 50 is the area in which a first device having a firstpolarity is built, while the second device region 52 is the area inwhich a second device having a second polarity that is opposite to thefirst polarity is built.

Next, a spacer 22 is formed in the opening 20 on the exposed sidewallsprovided by the above processing steps. The spacer 22 is formed bydeposition and etching. The spacer 22 can be comprised of an insulatingmaterial such as, for example, an oxide, nitride, oxynitride or anycombination thereof. The spacer 22 may be a single spacer, as shown, orit may comprise multiple spacers. The spacer 22 employed in the presentinvention should cover the sidewall of the second semiconductor layer16. The resultant structure including the spacer 22 formed into theopening 20 is shown in FIG. 4.

The thickness of the spacer 22 should meet the requirement of isolationspacing for an inter-well between nFETs and pFETs, which is mainlydetermined by lateral straggle of the high energy well implantation anddopant redistribution and interdiffusion at the well borders. Typically,the spacer 22 has a width as measured along the bottom surface fromabout 10 to about 1000 nm, with a width from about 50 to about 200 nmbeing even more typical. The insulating material of the spacer 22 shouldbe different from that of the hard mask 18 so that the hard mask 18 canbe removed selectively to the spacer 22 in a subsequent processing stepof the present invention. In accordance with the present invention, thespacer 22 is a first trench isolation region having a first depth thatis used in separating devices of different polarity from each other.

In some embodiments of the present invention (not shown), a deep wellimplant may be performed at this point of the inventive process into theopening 20, after spacer 22 formation. In such embodiments, theimplantation energy can be reduced because the ions have a shorterdistance to travel. Lower implantation energy corresponds to lesslateral struggle, which allows for less inter-well isolation spacing.

A semiconductor material 24 is then formed on the exposed surface of thefirst semiconductor layer 12 to provide the structure shown, forexample, in FIG. 5. In accordance with the present invention,semiconductor material 24 has a crystallographic orientation that is thesame as the crystallographic orientation of the first semiconductorlayer 12. Although the regrown semiconductor layer 24 will have the samesurface orientation as the first semiconductor layer 12, it can be of adifferent semiconductor material than the first semiconductor layer 12.

The semiconductor material 24 may comprise any semiconductor material,such as, for example, Si, strained Si, SiGe, SiC, SiGeC or combinationsthereof, which is capable of being formed utilizing a selectiveepitaxial growth method. Semiconductor material 24 can be strained,unstrained, or it can be comprised of stained and unstrained layers,e.g., strained Si on a relaxed SiGe layer.

In some preferred embodiments, semiconductor material 24 is comprised ofSi. In other preferred embodiments, the semiconductor material 24 is astrained Si layer that may or may not be located atop a relaxed SiGealloy layer.

To achieve a high quality regrown semiconductor layer 24, selectiveepitaxy is recommended where there is no polysilicon or amorphoussilicon formed on top of the patterned hard mask 18 outside the opening20. To eliminate a facet formation during the epitaxy, the semiconductormaterial 24 can be grown, in some embodiments, higher than the patternedhard mask 18 and then it is polished down to the patterned hard mask 18.

In other embodiments, the regrown semiconductor material 24 may berecessed at this point of the present invention utilizing a timedetching process such as a timed RIE. One or more additionalsemiconductor layers can be formed directly on top of the recessedsurface. The semiconductor materials formed would each have the samecrystallographic orientation as that of the first semiconductor layer12.

To achieve a coplanar surface, the semiconductor material 24 may need tobe etched back to the same level as the second semiconductor layer 16.This etching can be performed by dry etching, wet etching or oxidationof silicon and then stripping away the oxide. If there is little or nofacet growth, the thickness of the epitaxy material, i.e., semiconductormaterial 24, can be controlled by growth time so that the upper surfaceof the epitaxial material is substantially coplanar with the uppersurface of the second semiconductor layer 16.

In some embodiments of the present invention, the semiconductor layer 24can be formed by an in-situ doped epitaxial growth process. In-situdoping can achieve better control of the location of the dopant well,for example, the vertical dopant profile can be much sharper than theone obtained through implantation. Also, in-situ doping can reduce thetraditional problem of dopant redistribution and interdiffusion at thewell borders when both the n-well and the p-well are formed by ionimplantation.

The patterned hard mask 18 is now removed from the structure utilizing aconventional stripping process that is capable of selectively removingthe patterned hard mask 18 from the structure, especially to the spacer22. The structure that is formed after the patterned hard mask 18 hasbeen removed is shown, for example, in FIG. 6. In this structure, thefirst semiconductor device surface, i.e., second semiconductor layer 16,is substantially coplanar to the regrown semiconductor material 24.

After providing the structure shown in FIG. 6, standard CMOS processingcan be performed. First, a shallow trench isolation regions 26 areformed, where the trench depth is determined by the isolation oflike-type devices (see, FIG. 7) between nFET and nFET, and pFET andpFET. Note that the depth of the trenches of the shallow trenchisolation regions 26 is shallower than the depth of opening 20 and thusthe spacer 22. In accordance with the present invention, the shallowtrench isolation regions 26 form the second trench isolation regionshaving a second depth that is shallower than that of the first trenchisolation region, i.e., spacer 22. In case the spacer 22 has beenattacked during the hard mask 18 removal process, this shallow trenchisolation can also be formed between nFET and pFET, simultaneously.Shallow trench isolation used at this point of the present invention inthe dense area within like-kind devices, greatly simplify the isolationprocess.

The shallow trench isolation regions 26 are formed utilizing processingsteps that are well known to those skilled in the art including, forexample, trench definition and etching, optionally lining the trenchwith a diffusion barrier, and filling the trench with a trenchdielectric such as an oxide. After the trench fill, the structure may beplanarized and an optional densification process step may be performedto densify the trench dielectric.

Next, well regions (not specifically labeled) are formed into theexposed semiconductor device layers, i.e., layer 16 or the regrownsemiconductor material 24, by utilizing ion implantation and annealing,both of which are well known to those skilled in the art. The wellregions may be n-type well regions or p-type well regions depending onthe type of semiconductor device to be formed on each semiconductorlayer, i.e. second semiconductor layer 16 and regrown semiconductormaterial 24. For example, if the semiconductor device is a pFET, thewell region will be an n-type well, while if the semiconductor device isan nFET, the well region is a p-type well. Doping of each well isperformed in different implant steps in which an implant mask is formedatop locations in which the specific dopant is not intended to beimplanted into. The depth of the well regions can vary depending on theimplant and annealing conditions as well as the type of dopant used.

After well formation, semiconductor devices, i.e., pFETs and nFETs, areformed on the exposed semiconductor layers, i.e., second semiconductorlayer 16 and regrown semiconductor material 24. Specifically, a firstsemiconductor device 32 is formed on a portion of the secondsemiconductor layer 16 (in the first device region 50) and a secondsemiconductor device 30 is formed on the regrown semiconductor material24 (in the second device region 52). In accordance with the presentinvention, the first semiconductor device 32 may be a pFET or an nFET,whereas the second semiconductor device 30 may be an nFET or pFET, withthe proviso that the first semiconductor device is different from thesecond semiconductor device and that the specific device is fabricatedon a crystal orientation that provides a high performance device.

The pFETs and nFETs are formed utilizing standard CMOS processing stepsthat are well known to those skilled in the art. Each FET includes agate dielectric, a gate conductor, an optional hard mask located atopthe gate conductor, spacers located on sidewalls of at least the gateconductor, and source/drain diffusion regions. Note that the pFET isformed over the semiconductor material that has a (110) or (111)orientation, whereas the nFET is formed over a semiconductor surfacehaving a (100) or (111) orientation. The resultant structure includingbulk-like FETs is shown in FIG. 7.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method of fabricating a semiconductor structure comprising:providing a hybrid substrate comprising a first lower semiconductorlayer of a first crystallographic orientation and a second uppersemiconductor layer of a second crystallographic orientation whichdiffers from the first crystallographic orientation, wherein aconductive bonding interface separates said semiconductor layers fromeach other; providing at least one opening of a first depth in saidhybrid substrate which exposes said first lower semiconductor layer;forming a spacer having said first depth within said at least oneopening; regrowing a semiconductor material on an exposed portion ofsaid first lower semiconductor layer, said semiconductor material havingsaid first crystallographic orientation; planarizing said semiconductormaterial to an upper surface of said second upper semiconductor layer toprovide a structure having at least two coplanar surfaces of differentcrystallographic orientation; and forming trench isolation regionshaving a second depth which is shallower than the first depth withinsaid structure having the at least two coplanar surfaces of differentcrystallographic orientation, wherein said spacer isolates thesemiconductor material formed in said at least one opening from at leastthe second upper semiconductor layer, and wherein said second uppersemiconductor layer defines a first device region and said semiconductormaterial formed in said at least one opening defines a second deviceregion.
 2. The method of claim 1 wherein said providing said hybridsubstrate comprising a bonding process.
 3. The method of claim 2 whereinsaid bonding comprising contacting said two semiconductor layers at roomtemperature, optionally applying an external force and optionallyannealing.
 4. The method of claim 1 further comprising forming firstsemiconductor devices of a first polarity in said first device regionand forming second semiconductor devices of a second polarity thatdiffers from said first polarity in said second device region.
 5. Themethod of claim 4 wherein said first semiconductor devices comprisenFETs and the second semiconductor devices comprise pFETs, said nFETsare located on a (100) crystallographic surface and said pFETs arelocated on a (110) crystallographic surface.
 6. The method of claim 4wherein said first semiconductor devices comprise pFETs and the secondsemiconductor devices comprise nFETs, said nFETs are located on a (100)crystallographic surface and said pFETs are located on a (110)crystallographic surface.